Technical Abstract:
Aspergillus flavus is a pathogen of many agronomically important crops worldwide and can also cause human and animal diseases. A. flavus is the major producer of aflatoxins (AFs), which are carcinogenic secondary metabolites. In the United States, mycotoxins have been estimated to cause agricultural losses totaling upwards of $1.66 billion annually. In 1974, an AF poisoning epidemic resulted in 106 human deaths in western India, and more recently, in 2004, 125 deaths were reported in Kenya, East Africa. We recently described Petromyces flavus, the sexual state of A. flavus, from crosses between strains of the opposite mating type. We demonstrated that sexual reproduction in A. flavus is heterothallic and occurs between individuals belonging to different vegetative compatibility groups, which suggest that the vegetative compatibility system is not a barrier to genetic exchange and recombination. In the present study, we genetically examined the F1 offspring from several successful crosses. Linked loci within the AF gene cluster on chromosome 3 and unlinked loci on different chromosomes were analyzed to detect crossovers and independent assortment. Our data indicate that recombination increases the effective population sizes of aflatoxigenic fungi and may be driving genetic and functional hyperdiversity in A. flavus. We also observed non-Mendelian inheritance of extra-genomic AF cluster alleles in crosses with partial AF cluster parents, which suggests a possible role of cryptic heterokaryosis, in addition to sexual recombination, in modulating AF production.